Kinetic analysis of the interfacial reactions in Ni/Sn/Cu sandwich structures

Abstract

The mutual interaction between Sn/Ni and Sn/Cu interfacial reactions in a Ni/Sn/Cu sandwich sample has been studied. The major interfacial reaction product on the Cu side was Cu 6 Sn 5 , while on the Ni side, a ternary (Cu,Ni) 6 Sn 5 compound layer was formed. We found that the growth kinetics of the interfacial compound layers on both sides reached a steady state in the late reflow stage. The interfacial compound layer on the Cu side retained a constant thickness. On the other hand, the interfacial compound layer on the Ni side grew at a relatively fast rate, which was found to be linear with time. Our results indicate that the growth of the ternary (Cu,Ni) 6 Sn 5 compound layer was controlled by the Cu dissolution flux at the solder/Cu 6 Sn 5 compound interface. The dissolution constant of the Cu 6 Sn 5 compound into the molten Sn was determined to be 0.13 mm/s.

Suppressing the growth of Cu–Sn intermetallic compounds in Ni/Sn–Ag–Cu/Cu–Zn solder joints during thermal aging

“…This phenomenon is related to the amount of Ni and Zn inside L-(Cu,Ni) 6 (Sn,Zn) 5 . From Table 2, it is found that the Ni/SAC/CuexZn solder joint has higher Zn content in the CuexZn substrate, causing the higher Zn and lower Ni concentration within L-(Cu,Ni) 6 (Sn,Zn) 5 . The less Ni in the interfacial IMC implies the more Ni in the molten SAC solder near the interface.…”

“…However, H-(Cu,Ni) 6 Sn 5 was not altered, and L-(Cu,Ni) 6 (Sn,Zn) 5 grew slowly in the Ni/SAC/Cue15Zn. It is inferred that the Zn dissolving into L-(Cu,Ni) 6 (Sn,Zn) 5 restrained the Ni diffusion into L-(Cu,Ni) 6 (Sn,Zn) 5 . Literature pointed out that Zn or Ni atoms doping into Cu 6 Sn 5 can shrink the lattice volume [18,22].…”

“…Minor Ni from the Ni substrate dissolved into the solder, migrating toward the SAC/Cu interface during reflow. The dissolution of minor Ni decreased the Cu solubility in Sn [5,6], inducing that the L-(Cu,Ni) 6 Sn 5 IMC easily precipitated near the SAC/Cu interface [2]. So, it was observed that a loose and block-like L-(Cu,Ni) 6 Sn 5 layer formed at the SAC/Cu interface.…”

“…Ni atoms substituted the Cu sites in lattice, while Zn atoms substituted the Sn sites. The Cu 6 Sn 5 -based IMC with Ni and Zn is represented as L-(Cu,Ni) 6 (Sn,Zn) 5 . Literature indicated that the minor Zn doping into Cu 6 (Sn,Zn) 5 can decrease the Gibbs free energy and stabilize the hexagonal structure [22].…”

“…The cross-interaction was attributed to the diffusion of Cu and Ni atoms through the solder alloy from one side to the other side between Cu and Ni substrates [2e6]. Liu et al reported various microstructures and microhardness across the Ni/Sn/Cu sandwich structure during the reflow process [5,6].…”